There are two types of induction heating applicances. The first type is that in which a conventional power supply is converted by an inverter including a transistor, a thyristor, etc. into a high frequency current of about 20 KHz, for instance, and the resulting high frequency current is fed into a plate-like induction heating coil for the purpose of heating a pan or the like. The second type is that in which a low frequency current is supplied to a plate-like induction heating coil without converting it into a high frequency current. When an electrically conductive cooking pan is mounted over the induction heating coil on a top plate of insulating material, a magnetic flux is developed across the conductive pan to induce an electromotive force in the conductive pan which produces an eddy current. The eddy current, combined with the resistance of the conductive pan, generates heat and heats the conductive pan itself and thus the food to be cooked in the pan. Since the magnetic flux developed from the induction heating coil serves to heat the pan directly, this method has much smaller heat loss and higher efficiency than the conventional methods using firewood, gas, kerosene or an electric heater and reduces energy consumption to a minimum and makes a remarkable contribution to energy savings.
A way to improve cooking efficiency is to provide a plurality of the induction heating coils in the above mentioned type of the induction heating appliances but faces great difficulties in cooling the whole of the appliance.
FIG. 11 depicts flows of cooking air in a conventional cooking appliance having a coil B and a power supply P but with no partition therein. Since a small-sized axial-flow fan F used in such induction heating type cooking appliances generally can produce only a very small static pressure, the smaller the effective areas of air inlet and outlet ports the greater the resistance of incoming air and outgoing air and the difference in static pressure between the air inlet region of the fan in the cabinet space and the air outlet region. As a result, a reverse-current air circulation path (or short circuit circulation path) is formed in the cabinet space to thereby drastically reduce the efficiency of cool air intake and hot air exhaust. More especially, as shown in FIG. 11, the internal pressure at the air inlet region 36 of a cabinet C is negative relative to the internal pressure at the air discharge region 37 of the cooling fan F and pressure external of the cabinet (namely, the atmospheric pressure). The amplitudes of the pressures in the respective regions are in the relation: pressure of the region 37&gt;atmospheric pressure&gt;pressure of the region 36. Therefore the difference in pressure between the regions 37 and 36 is a maximum. As a result, a substantial amount of air flows in a reverse direction and circulates as indicated by the arrows in FIG. 11.
The cooling fan loses several tens of percent of its full capacity for a reverse flow and circulation of the hot air and undergoes a significant decrease in the efficiency of drawing in outside cool air and discharging hot air, thus sending a flow of air of elevated temperature relative to the atmospheric air to the solid state power converter unit. This results in a greatly decreased efficiency of cooling off the circuit components and therefore results in a need for a cooling fan of a higher capacity and a heat sink.